There appears to be a defined need for an implantable glucose sensor which would have multiple potential uses in clinical research and in improved therapy for diabetics, for example as part of a glucose monitor or, more distantly, as a component in an artificial electrochemical beta cell. For several years we have been developing an electrochemical glucose sensor. Our previous efforts have: 1) demonstrated that an electrochemical sensor utilizing a platinum glucose electrode is, in principle, feasible; 2) identified problems in need of solution; and 3) pointed out the need for more basic research before further advances can be made. We therefore propose an integrated research plan, the major thrust of which will be fundamental in character and will include further detailed in vitro characterization of the existing sensor and basic studies of glucose electrochemistry and individual electrode behavior. These studies will lead to design of improved and more reliable sensors which will then be further characterized by short-term and long-term in vitro testing. Smaller, concurrent efforts will be devoted to development and testing of needed electronics and telemetry equipment. We will initiate pilot animal implantation studies when the long-term in vitro results indicate that we have a sufficiently reliable and stable sensor so that critical questions regarding host tissue response can be answered.